Concrete progress

20 February 2009

Iter is progressing despite the global recession. Testing of prototype remote handling machines has started on a mock-up of the divertor region, while building foundations will be laid later this year. By Caroline Peachey and Keith Nuthall

Despite scepticism about its viability, the tough economic climate and the fact that it one of the largest, most complex scientific projects ever conceived, the international Iter project to build an experimental fusion reactor is moving forward.

A concrete step

The end of January saw inauguration of the Divertor Test Platform Facility (DTP2). Recently assembled in Tampere, Finland, this facility has taken four years to design and manufacture, at a cost of some r7 million ($9 million), half of which was funded by the Euratom programme. It is the culmination of efforts from scientists all over Europe, working together with four industrial partners based in Finland, Luxembourg and Spain.

Director general for research at Euratom, Octavio Quintana Trias, described the start of testing at DTP2 as: “another concrete step towards the realisation of a project that has been dreamed of for years.”

The divertor

The divertor is one of the key components that will be found inside the fusion reactor. Its function will be to extract heat, “helium-ash” – the products of the fusion reaction – and other impurities from the plasma, in effect acting like a giant exhaust pipe. It will comprise two main parts: a supporting structure made primarily from stainless steel and the plasma facing component, weighing about 700t in total. The plasma facing component will be made of a high refractory material such as tungsten-carbon fibre composite. Its exact composition has not been finalised but the material chosen must be able to withstand high electromechanical loads, allow high-vacuum pumping to remove the helium from the vacuum chamber, and tolerate long exposure to neutron radiation.

As the divertor will be a plasma facing component, subject to extreme conditions (the deuterium and tritium gases need to be heated to 100 million degrees centigrade for sustainable fusion) it will suffer from erosion. In fact, it is estimated that the divertor will need to be replaced at least three times during the reactor’s proposed 20-year lifetime. For maintenance purposes, the divertor will be made up of 54 sections or cassettes.

Since the conditions inside the vacuum containment – where the divertor will be located – will be harsh due to neutron radiation/tritium presence, it will be inaccessible to man. Therefore any maintenance or vital repairs must be carried out in a remote manner, which is where DTP2 comes in.

The maintenance process (all of which must be carried out remotely from a control room) for the divertor can be roughly divided into three main phases:

• Lift the cassette and carry it out of the vacuum vessel

• Take cassette 100m from the Tokamak building to the Hot Cell building using a fully automatic Cask System – an air-transport system capable of carrying 100t – where operators perform maintenance, using remote handing devices to inspect/repair/replace components.

• Return the cassette and precisely reinstall into the reactor.

The test facility

The main element of the DTP2 facility is the Divertor Region Mock-Up (DRM), a large structure that replicates the geometry of the lower part of Iter’s vessel and one radial port. The DRM provides the radial and toroidal rails to support the divertor cassettes, and the rails for remote handling equipment which carries out the divertor maintenance. Such equipment includes prototypes of the Cassette Multi-functional Mover (CMM) and the Secondary Cassette End Effector (SCEE). The CMM, weighing 65t, will run on a 20m supporting structure, transporting the divertor cassettes (9 to 10t each) along rails to and from Iter’s plasma chamber.

The maintenance operations that need to be carried out will be very demanding due to the weight of the components and the limited space. Operations will therefore require high position accuracy and heavy-load bearing, but compact actuators. Hydraulics meet these requirements, however the use of oil is not permitted in the fusion reactor as leakage could cause contamination to the vacuum vessel. For this reason water hydraulics have been chosen, while the sealants that will be used have been (and continue to be) tested in operational fission reactors.

The design and manufacture of the CMM and SCEE prototypes were carried out by the Spanish company Telstar Tecnologia Mecanica SL at its facility in Terrassa, near Barcelona. VTT Systems Engineering and Tampere University of Technology (members of the Finnish fusion association Tekes) constructed the mock-up that replicates a section of the Iter divertor region. The components used were manufactured by companies in Finland (TP-Konepajat Oy) and Luxembourg (Gradel SA). Here it is important to note that the plasma facing component, manufactured by Gradel SA, has been made of graphite in order to reduce costs. It has, however, been carefully engineered so that it will have the same dimensions and the same specific gravity as the component to be used in the reactor.

While the CMM was being constructed in Spain, scientists from Tampere University of Technology were developing and testing the software necessary to control it. This was achieved by linking the control hardware, supplied by a second Spanish company, Procon Systems SA, to a virtual model of the CMM.

Testing, testing

Now that the test platform facility has been assembled all elements of the remote handling activities can be studied and developed so that all (or at least most) of the possible problems already have a solution once real maintenance starts. It is important to remember that Iter is the experiment: remote handling is not!

Due to the harsh conditions inside the vacuum vessel, there will be a limited number of cameras. This means that the operators performing maintenance from a control room need to be thoroughly trained now, while they have access to the maintenance platform.

The control room layout is based on two operators and a supervisor. The operators have computer screens and in addition data is projected on the wall in front of the operators.

The operator control system for DTP2 combines camera information with calibrated graphical computer models so that the operator can get views required to drive the maintenance manipulators. Whilst moving, the position information of the manipulators is sent into a virtual model which is updated, essentially in real-time.Devices can be controlled by using joystick, keypad, or by pointing from the graphical user interface, and by a combination of these methods. The use of a computer model helps to ensure that the operator is staying in the allowed area or path and prevents unwanted collisions. Operators have now started a two-year testing phase.

A concrete example

The Iter project is truly an international one, with countries representing over half of the world’s population involved: the EU and Switzerland; India; Japan; China; South Korea; Russia; and the USA. Each party has its own significant fusion programme but the Iter project is first priority and proves that global collaboration can be successful.

Dider Gambier, director of Fusion for Energy, the European Union organisation responsible for providing Europe’s contribution to Iter, said: “DTP2 is a concrete example of successful cooperation between Fusion for Energy, European laboratories and industrial partners.”

According to the EU official, the project represents the largest scientific experiment ever attempted, in terms of financial and also organisational requirements. The total cost of the project was estimated at r10 billion in 2006 but “there will be cost increases, that is for sure,” according to Trias. He said that a group of experts has been asked to reassess the costs because they are based on an old design and commodity price are constantly fluctuating. A revised cost estimate is expected in November this year.

The financing of the project will be split as follows: the EU and Switzerland will contribute 45.45% of the required funds, and the remaining parties will contribute 9.09% each. Moreover each party has declared themselves ready to contribute 10% (50% in the case of Europe) and a de facto reserve has been created to deal with unexpected costs.

Fusion for Energy (F4E), with headquarters in Barcelona Spain, was created on 27 March 2007 with a life of 35 years, and will manage the EU budget of some r4 billion over the first ten years of the project.

A good investment?

With the current economic climate, research budgets are not secure, however experts stressed that continued investment is key to the project success. It will keep high-qualified specialists involved, improve technical knowledge in all of the member states, and could have many spin-off applications in other industries, not to mention the benefits to society if fusion power is successfully commercialised.

Iter will be financed by seven parties – including the EU with its 27 members – and the cost of the project will be spread over more than 30 years. When this is placed in context, for example in the EU it is less than the budget for the effort in renewable energies, it doesn’t seem such a bad investment.

The second purpose of the Iter project – to create knowledge or intellectual property in each of the partner countries – cannot only be quantified financially. Each of the parties will make each component (or a part of each of the components) in order to generate technical knowledge and expertise in every partner country. This project structure makes for complex planning and therefore higher costs, but according to its proponents it will be worth it in the end. It is hoped the Iter model will be comparable with that of the European Organization for Nuclear Research, CERN, where 38% of the technology contracts produced new products to the markets.

Pouring the concrete

In November the Iter Organization officially moved into its headquarters in Cadarache in the South of France. The 180ha site that will house the reactor has been cleared and is surrounded by a fence. The team are now working on getting water and electrical infrastructure to the site, so that excavation and construction of buildings can begin. Later this year the first concrete will be poured and so, by the end of 2009 construction on the largest international experiment will have made one more concrete step forward.

Total fusion power 500MWPower multiplication factor (Q)* 10Tokamak diameter 24mTokamak height 15mPlasma volume 850m3On-axis toroidal magnetic field 5.3TOperational life 20 years+*This means that the Iter experiment will generate ten times more power than is required to heat the initial hydrogen plasma

Procurement agreements approved

In November, five procurement agreements totalling u414.5 million were approved. These included a deal to build sections of a vacuum vessel in South Korea; to manufacture toroidal field magnet windings and structures in Japan; and the construction of the facility for winding of five of the six required poloidal field coils on the Iter site in France, financed by the EU. The EUR116 million vacuum vessel deal was particularly noteworthy given this is the double-walled steel container in which Iterâ€™s plasma will by contained by magnetic fields.A report from the organisation noted: â€œThe Iter vacuum vessel will be the biggest fusion furnace ever built: it will be twice as large and 16 times as heavy as any previously manufactured fusion vessel â€“ each of the nine torus shaped sectors will weigh about 450 tons. When all the shielding and port structures are included, this adds up to a total of 5,116 tons. Its external diameter will measure 19.4 metres, the internal 6.5 metres. Once assembled, the whole structure will be 11.3 metres high.â€Approval was also given for a so-called â€˜test blanket module programmeâ€™, which â€“ said an Iter noteÂ­ â€“ would â€œallow testing of concepts for achieving self-sufficiency in tritium supply for future fusion power-plants.â€Looking ahead, procurement agreements for developing Iter divertor plasma-facing components should be ready for signing this month, and for the cassette body in July 2009, according to Mario Merola, Iter divertor section leader.Meanwhile, as detailed computer modelling will be key to the success of the Iter project, a consortium of 14 research teams from across Europe has been formed to create a computer simulation of the fusion reactor to assess and test virtually the technology required to operate it safely. The EU-funded EUR3.65 million ($4.7 million) EUFORIA project will forge a network of high-powered computers with sufficient capacity to undertake this modelling, which will involve massive amounts of data.Its researchers will firstly adapt plasma physics and magnetic confinement fusion codes for use by multiple computer processors, speeding the solution of large problems. â€œWe try to link the different computer architectures such that the strengths of the respective architecture are made use of to the full extent,â€ Dr Marcus Hardt, project coordinator, from the Karlsruhe Research Centre (FZK) in Germany, told a European Commission note on EUFORIA. Research teams are based in France, Finland, Germany, Italy Spain, Poland, Slovenia, Sweden and Britain. Also, the Iter organisation and the Switzerland-based European Organization for Nuclear Research (CERN) have signed a cooperation agreement that will see CERN advising the new project regarding the technology and administration needed to run large-scale projects of this kind. CERN and Iter will cooperate in the use of technology such as superconductors, magnets, cryogenics, control and data acquisition and complex civil engineering, and regarding financing administration, purchasing, human resources, and sourcing and developing software programmes.A CERN-Iter steering committee has been established to further this work. Practical achievements from this alliance have thus far included preparing technical specifications for Iterâ€™s toroidal field coils; conducting tests for the poloidal field insert coil in Naka, Japan; and developing high temperature superconductor current leads (in cooperation with China).

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